Found this on the Federal Ammunition site. I don't know how old it is but here it is anyways.

NEW YORK'S FIFTY FIGHT . . . The ownership of a fifty caliber rifle would be outlawed in New York with passage of just one of many additional restrictions on firearms proposed in the legislature. The Fifty Caliber Institute encourages residents to contact legislators immediately to stop measures designed to outlaw the ownership of firearms based on their bore size.

Build memories, take a kid out doors and teach them about nature by interacting with it, hunting and fishing.

I don't know anyone who's got a 50cal either, but thats not the point. The ANTI's, whether they be anti-gun, or anti-hunting, start by outlawing equipment and practices on the fringes of a group, and slowly work towards taking away the rest. We can say that we don't have a need for a gun like that, and allow it to be outlawed, but eventually it'll get to the point where they are encroaching on your rights. England and Australia are good examples. Sportsman and Recreation shooters have to maintain a united front, or else anti's will divide, separate, and conquer.

The law most likely would exclude muzzleloaders, as the ATF does not classify them in the same sense of the terms, as rifles. This is how you can buy a muzzleloader through the mail, i.e. Cabelas, etc. Technically they are classifies as Antiques, not firearms.
I think the law in NY would intend to ban larger caliber firearms that are not meant for sporting purposes, such as certain handguns that can be bought over .50 cal.